The present invention relates to an improvement for an amplifier, and particularly to an amplifier circuit that provides increased dynamic range in polar modulation applications.
Competitive forces in the wireless communication industry are continuously forcing prices down and requiring higher data rates, especially for non-voice applications. To achieve lower costs, wireless communication device designers must reduce parts count as well as take advantage of economical components. Higher data rate requirements force higher performance from wireless communication devices. In addition to these pressures, wireless communication devices must operate very efficiently to reduce power consumption in an effort to maximize battery life.
Most of the power consumption in a wireless communication device takes place in the power amplifier circuitry. In an effort to maximize efficiency, power amplifiers must operate near peak efficiency over varying power ranges, which are required in most wireless communication architectures. In addition to controlling output power, certain communication architectures incorporate polar modulation, wherein part of the modulation scheme requires modulation of the supply voltages provided to the power amplifiers. Unfortunately, the dynamic range required for advanced wireless communication architectures, such as the Enhanced Data Rates for GSM Evolution (EDGE), requires the power amplifiers to provide output power over a significant dynamic range, such as 45 dB. These large dynamic range requirements have forced additional complexity and parts counts into these wireless communication devices. Further, the additional parts and complexity have led to less efficient operation.
Accordingly, there is a need for power amplifier circuitry in polar modulation applications that provides efficient operation in a cost-effective and easy to implement manner.
The present invention provides power amplification circuitry having multiple amplifier stages in series and adapted to facilitate polar modulation. As such, the amplifier circuitry receives a frequency signal representing the frequency and phase components of the signal to be transmitted, as well as an amplitude signal presenting the amplitude component of the signal to be transmitted. The frequency component is amplified by the amplification circuitry. The amplitude component controls the supply voltage provided to the amplifier stages in the amplification circuitry. To increase the dynamic range of the amplification circuitry, the final stage or stages of the amplification circuitry are selectively disabled when lower output powers are necessary, and enabled when higher output powers are required. When disabled, the output stage is biased in a manner such that it effectively functions as a series capacitor, coupling the amplified signal from the prior amplifier stages through the final output stage to an antenna for transmission.
Preferably, the transistors forming the output stage or stages are disabled by allowing the collectors or drains, as the case may be, to float, while the base or gate remains biased. Application of a constant bias to the base or gate of the output stage transistors provides a constant load for the previous stages and allows the devices to effectively operate as a capacitor. As such, when the output stage is disabled, the prior amplifier stages can operate at more efficient levels while providing lower output powers.